The aims of this study were to determine the effect of the quality of
sugar cane juice (sugar concentration), as influenced by season of harvesting, on the
performance of fattening pigs given this feed as the basis of their diet. The hypothesis
to be verified was that the feeding value of the juice for pigs would be lower for sugar
cane harvested in the rainy season compared with cane harvested in the dry season.

The sugar cane used in the experiment had been planted at monthly
intervals between July 1994 and 1995 in plots measuring 800 m². There were two treatments
applied in each of two trials which were carried out consecutively in the wet and dry
seasons. The treatments were: SCJ: Sugar cane juice and protein supplement; Control:
Broken rice and protein supplement. The trials were done with different lots of pigs from
July 1995 to November 1995 (Trial 1; wet season) and from December 1995 to May 1996 (Trial
2: dry season). Four groups each of 3 crossbred pigs (Large White x Mong Cai) were
allocated to each of the two treatments in each of the trials. The initial weight at the
start of each trial was 20 kg on average and the trial continued until the pigs reached an
average of 70 kg liveweight (trial 1) and 65 kg liveweight (trial 2).

There were marked differences in the sugar content of the juice which
was 40% higher in the cane stalk harvested in the dry season (°Brix of 22) than in the
wet season (°Brix 16). Intake of juice was higher in the wet season but not enough to
compensate for the lower brix content as intake of sugars was 1.05 kg/d in the wet season
compared with 1.22 kg/d in the dry season. The growth rate of pigs fed cane juice in the
wet season was 28% lower than for those fed the control diet and 20% lower than for pigs
fed cane juice in the dry season. In both seasons the feed conversion rate was worse for
sugar cane juice than for the broken rice. Pigs fed cane juice in the wet season had
fatter carcasses than the control animals but there were no differences between diets in
the dry season.

The lower content of sugars (°Brix) in the juice appeared to be the
reason for the lower growth rates and fatter carcasses of pigs fed juice from wet season
cane.

Sugar cane is a crop with very high potential for biomass production.
It can be envisaged as a multipurpose crop with an important role in animal production.
Much of the research into sugar cane feeding has been conducted and has largely been
confined to studies with cattle and pigs (Preston 1995). It was confirmed that sugar cane
juice can completely replace cereals as the major energy source in diets for pigs (Mena
1981, Mena et al 1982; Figueroa 1989; Sarria et al 1990; Speedy et al 1991;
Bui Huy Nhu Phuc et al 1994; Le Thi Men et al 1996).

The decision to use sugar cane to make sugar or to feed animals will
depend on the relative prices of sugar and animal product, which in turn will be
influenced by the locality where sugar cane is grown. In the areas where sugar cane is
traditionally grown and processed into sugar the alternative use for livestock feed will
be attractive in situations where local processing is difficult and the nearest sugar
factory is some distance away (Nguyen Thi Loc et al 1992; Oanh 19..; Le Viet Ly and
Luu Trong Hieu 1994). This has been confirmed in the provinces of Tuyen Quang, Bac Thai
and Cao Bang in North Vietnam where it has been shown clearly that there is strong
incentive to use sugar cane juice in livestock feeding systems (Nguyen Thi Oanh 1994;
Hoang Thi Tham - Hoang Thi Tao 1996; Mai van Sanh et al 1996).

It is important to do more research on the use of sugar cane as
livestock feed since the requirements are different from those which apply when the end
purpose is production of sucrose. In the latter case a high concentration of sucrose in
the juice is essential in order to reduce the cost of processing since there will be less
water to evaporate and a higher yield in the factory of sucrose as percent of cane. To
achieve these conditions the harvesting of sugar cane for sucrose production is restricted
to the period of the year when the climatic conditions favour accumulation of sucrose; for
example when there is little rain (dry season) or a low temperature. Usually the actual
harvest period lasts only for some 4-6 months. In contrast, for livestock production, a
year-round supply of feed is required.

Most of the research with sugar cane for livestock feeding has been
based on its use during the traditional harvest season when sugar content (°Brix) of the
cane is highest. This has been based on the belief that feeding value would be directly
related to sugar content. On the other hand, some reduction in animal performance might be
acceptable when weighed against the advantages of having access to sugar cane throughout
the year.

The principal objective of the research to be reported here was to
determine the effect of the quality of sugar cane juice (sugar concentration), as
influenced by season of harvesting, on the performance of fattening pigs given this feed
as the basis of their diet. The hypothesis to be verified was that the feeding value of
the juice for pigs would be lower for sugar cane harvested in the rainy season compared
with cane harvested in the dry season. The eftects of month of planting and of harvesting
on biomass yield and °Brix of the juice are reported in a companion paper (Nguyen Thi Mui
et al 1996).

Materials and methods

Treatments, design and animals

The sugar cane used in the experiment had been planted at monthly
intervals between July 1994 and 1995 in plots measuring 800 m². It was estimated that
approximately 300 kg of cane stalks were available daily for harvesting throughout the
year and that this could provide enough juice (150 litres/day) to cover the needs of 12
pigs (about 8 litres/pig/day).

There were two treatments applied in eachof two trials which were
carried out consecutively in the wet and dry seasons. The treatments were:

SCJ: Sugar cane juice and protein supplement

Control: Broken rice and protein supplement

The trials were done with different lots of pigs from July 1995 to
November 1995 (Trial 1; wet season) and from December 1995 to May 1996 (Trial 2: dry
season).

Four groups each of 3 crossbred pigs (Large White x Mong Cai) were were
allocated to each of the two treatments in each of the trials. The initial weight at the
start of each trial was 20 kg on average and the trial continued until the pigs reached an
average of 70 kg liveweight (trial 1) and 65 kg liveweight (trial 2).

Feeding and management

Trial 1:

Feeding with sugar cane juice and broken rice began on 25 June 1995
with an adaptation period of 1 month to accustom the pigs to the new feeds and give them
time to reach the starting weight of 20 kg. Sugar cane stalks were harvested every third
day from the trial area beginning with the plots established in July 1994 and ending with
the plots planted in November 1994. Harvesting was arranged to ensure that the sugar cane
juice that was fed came from cane stalks planted 12 months earlier.

The juice was extracted twice daily (8:00-10:00 am and 3:00-5:00 pm) by
passing the stalks three times through a 2-roll crusher driven by a buffalo. It was
offered ad libitum three times daily at 10:00 am, 1:30 pm and 6:00 pm, in approximately
equal amounts at each feed.

The protein supplement contained (%w/w): fish meal 25, groundnut cake
75 and was fed at the rate of 500 g/pig/day (approximately 200 g/day of protein) according
to the recommendations of Sarria et al (1991). The control diet consisted of broken
rice grains fed ad libitum and the same protein supplement. Sweet potato vines were
given at the rate of 1 kg (fresh basis) per pig per day on both treatments.

Measurements

The concentration of sugars in juice (°Brix) was determined daily with
a hand refractometer. The pigs were weighed at the start of the trial and every 20 days.
Feed offered and refused was recorded daily. Samples were taken to determine dry matter
and nitrogen by conventional methods. The quality of the carcass was assessed in terms of
yield of the dressed carcass as a percentage of the liveweight at slaughter, the eye
muscle area and thickness of the back fat at the 3rd, 10th and 13th rib.

Results and discussion

Data on the composition of the feeds are given in Table 1. There were
marked differences in the sugar content of the juice which was 40% higher in the cane
stalk harvested in the dry than in the wet season. Protein content of the sweet potato
vines was higher in the wet season and the dry matter content was lower.

Overall treatment effects are shown in Table 2. The pigs readily
consumed the sugar cane juice and there was no problem of digestive upsets except for a
few cases of diarrhoea in the first days of the experiment.

Table 2: Effect of
sugar cane juice from cane harvested in the wet and dry season on growth performance of
the pigs (12 pigs per treatment)

Wet season

Dry season

Juice

Rice

SE/P

Juice

Rice

SE/Prob

Days of expt.

105

105

89

89

Live weight, kg

Initial

22.7

22.6

22

21.5

Final

67

80.3

66.3

65.2

Gain, g/day

405

560

±20/0.001

503

501

±15/0.1

Feed intake, kg/day

Juice

7.5

-

5.54

-

(sugars)

1.05

1.22

Broken rice

-

1.47

-

1.03

DM

1.78

1.81

±0.012/0.06

1.61

1.30

±0.03/0.001

N x 6.25

0.191

0.275

±0.001/0.001

0.176

0.230

±0.003/0.001

Feed conversion, kg DM/

kg gain

4.2

3.25

±0.17/0.007

3.16

2.54

±0.15/0.042

Intake of juice was higher in the wet season but not enough to
compensate for the lower °Brix content as intake of sugars was 1.05 kg/d in the wet
season compared with 1.22 kg/d in the dry season.

The growth rate of pigs fed cane juice in the wet season was 28% lower
than for those fed the control diet and 20% lower than for pigs fed cane juice in the dry
season. In both seasons the feed conversion rate was worse for sugar cane juice than for
the broken rice. Similar findings were reported by Figueroa (1989) in comparisons of maize
versus high test molasses (cane juice clarified, partially inverted and
concentrated) fed to growing pigs. Ly (1996) attributed this difference to higher losses
of energy in the metabolism of fructose which accounts for 50% of the digestible energy in
molasses; in contrast, the digestion of starch as in rice and maize yields only glucose.
The higher intake of protein on the rice diet compared with the juice diet, in both
seasons, could also have contributed to the better feed conversion on the former diet.

Carcass evaluation

The data on carcass quality are shown in Table 3. There were no
differences between the two treatments in carcass yield, carcass length or backfat
thickness. There was an indication of greater eye muscle area in favour of the pigs fed
broken rice.

Table 3: Mean values
for carcass yield, length, back fat and loin area (LA) adjusted by covariance for live
weight at slaughter

Wet season

Dry season

Juice

Rice

SE/Prob

Juice

Rice

SE/Prob

Yield, %

83.4

83.8

±1.2/0.86

72.5

74.4

±1.1/0.31

Length, cm

65.1

64.8

±0.86/0.84

59.3

59.8

±0.61/0.59

Backfat, mm

3.47

3.19

±0.41/0.35

3.91

3.94

±0.14/0.93

LA, cm2

27.7

31.8

±1.5/0.20

29.6

31.7

±0.65/0.11

In the wet season, the pigs fed cane juice tended to have a lower
percentage of lean meat and had a higher percentage of fat than those fed broken rice
(Table 4). There were no differences between treatments for the trial done in the dry
season. The proportion of skin was not influenced by diet. The data for organ weights
(Table 5) show few differences due to diet, other than the weights of the small intestine
which were less in pigs fed cane juice than in those fed broken rice (P=0.001 and 0.34 for
wet and dry seasons respectively).

Table 4: Mean values
for lean, fat, bone and skin in valuable cuts as percentage of carcass weight, adjusted by
covariance for liveweight at slaughter

Data on chemical composition of the loin eye muscle and the iodine
index of side fat are given in Table 6. There were no differences due to dietary treatment
apart from the ether extract in the eye muscle which, in the wet season, was higher for
pigs fed juice compared with rice.

Table 6: Mean values
for chemical composition of loin eye muscle and iodine index of side fat adjusted by
covariance for carcass weight

Wet season

Dry season

Juice

Rice

SE/Prob

Juice

Rice

SE/Prob

Composition of loin eye
muscle, %

DM

29.1

25.6

1.1/0.14

26.6

26.5

0.35/0.33

Protein

19.0

19.3

1.5/0.80

18.6

19.2

0.51/0.52

EE

6.84

8.68

0.087/0.001

5.41

4.96

0.33/0.42

Ash

1.13

1.20

0.092/0.67

1.03

1.03

0.013/0.9

pH

5.29

5.37

0.042/0.33

5.48

5.29

0.14/0.43

Side fat

Iod. index

55.1

59.5

1.1/0.09

50.3

49.9

1.05/0.83

Conclusions

Sugar cane juice derived from cane stalks harvested in the wet season
supported 20% lower growth rates in pigs than juice from cane harvested in the dry season.
Pigs fed the control diet of broken rice grew at similar rates in both seasons. In the dry
season pig growth rate on cane juice was the same as on broken rice.

In the wet season the carcasses of pigs fed sugar cane juice were
fatter than those fed broken rice. In the dry season, carcass quality did not differ
between diets. The content of sugars (°Brix) was 40% higher in the juice from cane stalks
harvested in the dry season than in juice from wet season cane. This appeared to be the
reason for the lower growth rates and fatter carcasses of pigs fed juice from wet season
cane.

Acknowledgements

This researched was supported by the International Foundation for
Science through a grant (B/2291-1) to the senior author.